linux-kernel - Re: [uml-devel] [UM] Long loop in __getnsdayoftime() after resume from ram

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Date:	Mon, 20 Oct 2014 10:27:50 +0200
From:	Richard Weinberger <richard.weinberger@...il.com>
To:	Thomas Meyer <thomas@...3r.de>
Cc:	user-mode-linux-devel <user-mode-linux-devel@...ts.sourceforge.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [uml-devel] [UM] Long loop in __getnsdayoftime() after resume
 from ram

On Sun, Oct 19, 2014 at 2:39 PM, Thomas Meyer <thomas@...3r.de> wrote:
> Hello,
>
> in UML kernel I get a long cpu using loop in __getnstimeofday()
> (kernel/time/timekeeping.c:315) in the call of timespec_add_ns(),
> when I left the host kernel suspended to ram for a few hours and resume
> again.
> this is because it seems like the tk->xtime_sec wasn't updated yet, but
> the nsecs were. nsecs can be as high as 8111000111000111000l
>
> the function timespec_add_ns() (include/linux/time.h:266) will call
> __iter_div_u64_rem() which has an optimized loop for the case
> that the dividend is not much bigger as the divisior.
> but this isn't the case for resume from ram on the host kernel.
>
> any ideas how to fix this? is it possible to intercept the resume from
> ram and update the timekeeper->xtime_sec somehow?
> or can the um arch somehow overwrite timespec_add_ns() to always use
> div_u64_rem() instead?

Hmm, does this always happen?
At least on my notebook it did not happen. I've started an UML yesterday
suspended it and after more than 12h it worked fine today.

BTW: Do you see the issue also then freezing UML using the freezer cgroup?
Would be easier to debug. :)

-- 
Thanks,
//richard
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